LM3477: Is the compensator network required as a default in the LM3477?

Dario Antonio Quintero Dominguez

Part Number: LM3477

For a standard buck design, is the compensator network required as a default in the LM3477?

The datasheet mentions:

"With the power stage known, a compensator can be designed to achieve improved performance and stability. The LM3477/A will typically require only a single resistor and capacitor for compensation, but depending on the power stage it could require three or four external components"

"COMP/SD 2 Compensation pin. A resistor-capacitor combination connected to this pin provides compensation for the control loop. Pull this pin below 0.65V to shutdown."

Could I just leave the COMP pin floating and would the buck regulator work without compensation?

over 3 years ago

0 Alec Biesterfeld over 3 years ago

TI__Expert 5310 points

Hello,

The LM3477 will require a minimum of an external resistor/capacitor tied between the COMP pin and ground. This will introduce a pole that will cancel out the ESR zero of the output filter and ensure the loop bandwidth falls within the 10kHz-50kHz band recommended for the LM3477 . If using a simple RC compensation scheme, R_c can be selected to satisfy equation 44 in the datasheet. C_c can then be selected in accordance with the relation demonstrated in equation 45.

Regards,

Alec Biesterfeld

0 Dario Antonio Quintero Dominguez over 3 years ago in reply to Alec Biesterfeld

Prodigy 20 points

Hi Alec,

Brilliant thanks! Just to check, on an inverting buck-boost topology, these resistor-capacitor combination must be tied down to the inverting voltage output rather than the system ground as below?

+1 Alec Biesterfeld over 3 years ago in reply to Dario Antonio Quintero Dominguez

TI__Expert 5310 points

Hi Dario,

Yes, that is the correct connection.

Regards,

Alec

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LM3477: Is the compensator network required as a default in the LM3477?